The present invention relates to a hydrostatic power transfer system which utilizes one or more hydraulically driven motors to drive vehicle wheels, ship turbines, or the like. Prior art arrangements have an energy source, such as an internal combustion engine, to drive a piston pump, which in turn pumps the fluid to hydraulic motors driving vehicle wheels or other power output devices, such as ship turbines and the like.
Historically known advantages suggest the use of pumps and hydraulic motors as essentially gearless infinitely variable torque/speed transmission systems for, for instance, automotive vehicles and ships. For example, one advantage is the possibility of permitting the pump to be driven by a combustion engine operating within a relatively highly efficient predetermined narrow torque-speed range with variations in the vehicle driving speed being accomplished by varying the displacement and/or speed of the pump and/or hydraulic motor or motors, rather than by varying the engine speed over a wide range. Smaller, lower horsepower rated engines, can thus be used for a given drive requirement.
Avoiding the necessity of significant acceleration and deceleration of the multiple parts of the prime mover internal combustion engine by maintaining a narrow torque-speed range results in better vehicle acceleration control by minimizing inertia effects. Also the combustion engines may be operated highly efficiently if they are permitted to operate in a pre-determined maximum efficiency ideal speed and torque range. The efficiency of gas turbine engines and reciprocating piston diesel engines can be substantially improved by operating in such predetermined ideal speed and torque ranges. Not only the efficiency as regards use of fuel, but also improvements in the reduction of the atmospheric contaminants by the exhaust gas can be achieved. Also, operation of such engines in a narrow torque/speed range substantially improves performance as regards bearing wear and the like because optimum bearing designs can be established for such ranges and stresses due to the minimization of torque fluctuations. U.S. Pat. No. 3,709,104 to Culbertson generally discusses certain of the advantages of using rotary piston pump transmission arrangements.
Reference is also made to my prior U.S. patents showing various pump configurations, namely U.S. Pat. No. 4,215,624 issued Aug. 5, 1980, U.S. Pat. No. 4,165,677 issued Aug. 28, 1979, and U.S. Pat. No. 4,161,906 issued July 24, 1979.
Although the idea of a hydrostatic transmission using piston pumps and hydraulic motors is relatively old, such as for automotive vehicles, successful commercial embodiments have yet to be developed due to various problems. One problem with using piston pumps is that there is a tendency to misalign the rotary shafts, pistons and cylinders of the pumps irrespective of various measures taken to prevent this, the transmission of varying engine torque results in undue wear on the pump assembly. Also, misalignment between pistons and cylinders results in thrust bearing wear problems. Furthermore, relatively large volume high pressure and high speed pumps are required, creating efficiency problems due to inherent low efficiency of such high pressure piston pumps. Further problems relate to non-laminar flow effects and mechanical vibration that the combustion engine driven piston pump causes in the transmission drive train.